1. Field of the Invention
The present invention relates generally to pulse compression and more particularly to pulse compression in the frequency domain whereby an output pulse is generated having the same pulse width as the phase coded input pulse but having a spectrum narrower than the phase coded pulse spectrum by a ratio equal to the reciprocal of the pulse width of the coded pulse.
2. Description of the Prior Art
Time domain pulse compression has been found to have particular utility in radar systems. In such systems, a comparatively long pulse is transmitted relative to the range resolution desired. When the echo of the transmitted pulse is received, a compression to the more desireable narrow pulse width is accomplished utilizing conventional time domain pulse compression techniques. Such techniques allow the range resolution accuracy attendant with narrow pulse widths at the high average power levels possible with long transmitted pulses. As a consequence, the pulse generating difficulties inherent with narrow pulses having high peak energies and are avoided.
In time domain pulse compression systems, the transmitted pulses are phase coded by linearly modulating the carrier frequency about a center value during the duration of the pulse transmission period or superimposing a pseudorandom phase coding on the transmitted pulse. In the receiver system, the coded signal is demodulated by passing it through a filter which is matched to the particular transmitted signal modulation code. Such a technique is described widely in the literature including "The Theory and Design of Chirp Radars" by J. R. Klander, A. C. Price, S. Darlington, W. J. Algersheim in Bell System Technical Journal, Vol. 34, July 1960 at pages 754-808; in Radar Signals An Introduction to Theory and Application by C. E. Cook, M. Burufeld, published by Academic Press; and in U.S. Pat. No. 3,686,572 entitled Pulse-Compressor System. Time domain pulse compression is thus a well known technique which decreases the demodulated (decoded) signal pulse width by a factor of the reciprocal of the bandwidth with the spectrum of the coded input and the decoded output being equal.
Although time domain pulse compression has many applications, situations arise in which the required matched filter cannot be utilized or the phase parameters of the received signal are not known. In addition, it may be preferable to demodulate the coded signal without down converting and passing through the matched filter required in time domain pulse compression systems.